1. Field of the Invention
This invention relates to high temperature heating vessels and, in particular, to reducing the degradation of a heating vessel lid in a glass melting furnace due to hot corrosive material reacting with the lid material.
2a. Technical Considerations
Continuous glass melting processes conventionally entail depositing pulverulent batch materials into a pool of molten glass maintained within a tank-type melting furnace and applying thermal energy until the materials are melted into the pool of molten glass. A melting tank conventionally contains a relatively large volume of molten glass so as to provide sufficient residence time for currents in the molten glass to affect some degree of homogenization before the glass is discharged to a forming operation. These recirculating flows in a tank-type melter may result in inefficient use of thermal energy. Conventional overhead radiant heating is inefficient in that only a portion of its radiant energy is directed downward towards the material being melted. Furthermore, attempting to heat a relatively deep recirculating mass of glass from above inherently produces thermal inhomogeneities which may carry over into the forming process and possibly affect the quality of the glass products being produced.
As an alternative to conventional tank-type glass melting furnaces, as described above, U.S. Pat. No. 4,381,934 to Kunkle and Matesa discloses an intensified batch liquefaction process in which large volumes of batch are efficiently liquefied in a relatively small liquefaction vessel. This type of process, particularly when using intensified heat sources, produces relatively small volumes of high temperature exhaust gas. Heat from this exhaust gas can be recovered and used to directly heat a batch stream feeding the liquefaction vessel so as to improve the overall efficiency of the process.
It is believed that during the batch melting process, certain components of the batch material may become vaporized and may combine with the exhaust stream along with any particulate matter that may become entrained in the exhaust. In the high heat environment of the liquefaction vessel as disclosed in U.S. Pat. No. 4,381,934, these vapors and particulates are highly corrosive. As the hot exhaust gas is removed from the top of the vessel, exhaust gas flow patterns may become established that tend to recirculate the corrosive gas in the vicinity of the lid of the vessel. These materials may corrode with the lid material causing degradation of the inner surface of the lid, leading to accelerated wear and premature replacement of the lid.
It would be desirable to control the circulation of the exhaust gas to keep it away from the lid so as to reduce lid degradation and increase lid life.
2b. Patents of Interest
U.S. Pat. Nos. 4,375,236 and 4,506,726 to Tsai teach the use of air jets to redistribute the combustion air and/or exhaust gas flow in a regenerative furnace for melting glass. Air jets positioned in the regenerators modify gas flow so that gas passing through the packing is evenly distributed throughout the packing to prevent localized overheating.
U.S. Pat. No. 4,496,315 to Savolskis and U.S. Pat. No. 4,496,316 to Tsai teach the use of air jets for controlling the flow of air into the melting chamber of a regenerative furnace. The jets are associated with firing ports and are used to increase the air flow from the regenerator into the melting chamber through selected firing ports.
U.S. Pat. No. 3,165,301 to Riviere teaches the use of fuel-oil injectors in the roof of an industrial furnace to protect its exposed refractory surfaces. The injectors produce a flow of carbon particles in a gaseous suspension along the roof of the furnace chamber in a direction opposite to a flame formed by a burner along the hearth portion of the furnace chamber. The carbon particles protect the roof refractory against the degradating effect of the heat radiating from the flame of the burner and the melted charge material.
U.S. Pat. Nos. 3,734,701 and 3,837,832 to Pecoraro et al teach the use of a burner in the refiner zone of a glass processing furnace to avoid tridymite-frost stone defects in float glass. The burners keep alkali vapors formed by the molten glass from contacting the silica crown of the furnace. It is preferred that the gas introduced at the refiner by the burner be hot, preferably within 50.degree. F. of the temperature of the glass in the furnace.